We're no longer receiving emails when a submission comes through.

I checked the email history for your account and did not see any failed emails.  You can view the same logs on your end:

https://www.jotform.com/help/293-How-to-View-All-Your-Form-Email-History

Check your spam/junkmail folder to ensure the emails are not being filtered there.  If they are, mark them as "not spam" or your email providers equivalent and they should no longer be filtered.